Hydraulic apparatus for operating machine tools and the like



Dec. 3, 1940. W P, MUER 2,223,792

HYDRAULIC APPARATUS FOR OPERATING MACHINE TOOLS AND THE LIKE Filed Aprill2, 1938 5 Sheets-Sheet l i W.P.MUIR Y .QMWM

ATT() RNEY Dec. 3, 1940. W P. Mum 2,223,792

HYDRAULIC APPARATUS FOR OPERATING MACHINE TOOLS AND THE LIKE Filed Aprill2, 1938 5 Sheets-Sheet 2 INVENTOR WRMUIR AT TORNEY W. P. MUIR Dec. 3,1940.

HYDRAULIC APPARATUS FOR OPERATING MACHINE TOOLS AND THE LIKE Filed April12, 1938 5 Sheets-Sheet 3 INVENTOR wan/lum ATTOB/NEY Dec, 3, 1940. W. P.MUIR 2,223,792

HYDRAULIC APPARTUS FOR OPERATING MACHINE TOOLS AND THE LIKE Filed Aprill2, 1938 5 Sheets-Sheet 4 L5.. n 5i in ll $1 9D @l 2 M. s $4 'l fil *2Ql I I? EB FH Q 1, :f 4| v )Il Il o I oo b4 @g a @a f il O l 1 O s' CD,It @im n r 'l :a

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vINvEN'roR WP.MUR

BY @M ATTORNEY WQP. MUIR 2,223,792

HYDRAULIC APPARATUS FOR OPERATING MACHINE TOOLS ND THE LIKE Dec. 3,1940.

Filed April l2, 193B 5 Sheets-Sheet 5 @OA w@ l NVENTOR W13. MUR

ATTORNE Patented Dec. 3, 1940 UNITED STATES PATENT OFFICE HYDRAULICAPPARATUS FOR OPERATING MACHINE TOOLS AND THE LIKE Application April 12,1938, Serial N0. 201,576

8 Claims. (Cl. 121-45) This invention relates to hydraulic apparatus foroperating machine tools and the like.

The said apparatus is characterized by a novel mode of operation whichcomprises applying pressure to move the tool in a given direction;

increasing said pressure when the tool has travelled a predetermineddistance, and utilizing the increased pressure to reverse the directionof travel of the tool. This method may be applied lo to effect eitherimmediate or delayed reversal of the tool in response to the rise ofworking pressure acting thereon. In the case of immediate reversal theincreased pressure is preferably utilized to open a normally closedpassage leading I5 to a reversing valve which then operates in directresponse to such pressure to establish hydraulic connections resultingin reversal of the direction of travel of the tool. In the case ofdelayed reversal, operation of the reversing valve by the 0 increasedWorking pressure is prevented by an opposing hydraulic pressure untilthe travel of the tool is halted by a mechanical stop. When this occursfthe opposing pressure is released or decreased suiciently to permitoperation of the 2r, reversing valve by the working pressure actingthereon.

Hereto the movement of tables on machine tools actuated by hydraulicmeans has been limited by the inability of the hydraulic system to :mcontrol the movements up to a predetermined point in the travel withabsolute accuracy. The control of reversal of travel of the table was bymeans of cams reversing the main control valve directly or through apilot valve, and it has been 3,-, found impractcable to use a definitemechanical stop for the table travel with the positive assurance thatthe table will contact this stop every time and not reverse its motionuntil it does so.

40 With the system described herein, definite assurance that the tablewill come to some positive l accurate stop so that it will be possibleto mill, plane or grind right up to a shoulder or radius Without leavinga relief or undercut for the tool to work into and thereby eliminatingthe extra operation to machine this relief or undercut and the weaknessto the piece entailed by theundercut.

Several samples of apparatus, illustrating dif- 50 ferent Ways ofeffecting hydraulic operation of machine tools or tables in accordancewith the novel principles of this invention, are shown and described inthe present application. It will be understood, however, that theprinciples involved 65 may be embodied in various other forms ofapparatus for operating machine tools, tables or any other movableelements to which the invention is usefully applicable.

' In the preferred embodiment of the invention, the working pressuremoves the tool against an opposing hydraulic pressure which isautomatically increased When the tool has travelled a predetermineddistance. This increase of pressure opposing movement of the tool causesa corresponding increase of working pressure which is utilized, aspreviously explained, to effect either immediate or delayed reversal ofthe direction of movement of the tool. When the increased workingpressure is to be utilized for eilecting immediate operation of thereversing valve the increase of pressure opposing movement of the toolby the working pressure merely serves to cushion the movement of thetool toward the end of its stroke and to cause the necessary increase ofworking pressure. When reversal of the tool is to be delayed until thetool is halted by a mechanical stop the increase of pressure opposingmovement of the tool is utilized to prevent operation of the reversingvalve by the increased working pressure until such time as the toolactually engages the stop.

A characteristic feature common to several forms of apparatus disclosedherein is the application of hydraulic pressure to move a tool against amechanical stop which, in addition to halting the tool after it hastravelled a predetermined distance, also serves, by its resistance tofurther movement of the tool, to promote establishment of pressureconditions resulting in hydraulic reversal of the tool. This employmentof a mechanical stop controlling both the working stroke and thereversal of the tool enables the point to which the tool is advanced atthe end of the working stroke to be predetermined within sufficientlyclose limits to meet the demands of any operating conditions likely toarise.

As a general rule it is not necessary that the return stroke of ahydraulically actuated tool becontrolled and predetermined within thesame close limits as the working stroke. Consequently, apparatusprovided in accordance with this invention may be designed so that thetravel and reversal of the tool during a working stroke is closelyregulated by a mechanical stop, as previously explained, while thereversal of the tool at the end of a return stroke is controlled solelyby an increase of the pressure then acting to move the tool. In othercases, where the limits within which both the working and return strokesmust bepredetermined are fairly wide, the reig'ersal of the tool afterit has travelled a predetermined distance in either direction may be'made dependent solely on an automatic increase of the pressure which isthen acting on the tool. In still other cases, where extreme accuracy isrequired in respect to controlling both the Working and return strokesof the tool, ythe latter may be operated against a stop at each end ofits travel so that the resistance of the stop serves, as previouslyexplained, to control both the stroke and the reversal of the toolwithin very close limits.

Proceeding now to a more detailed description reference will be had tothe accompanying drawings in which- Figure 1 is a view, mainly invertical section, of one form of apparatus by which the invention may bereduced to practice.

Figures 2 to 4 inclusive are views similar to Fig. 1 but showing otherpositions to which the valves and other component parts are shiftedduring operation of the apparatus.

Figure 5 is a vertical sectional view along the line 5-5 of Fig. 2.

' Figure 6 is a vertical sectional view along the line 6-6 of Fig. 2.

Figure '1 is a view similar to Fig. 1 but showing a modified form ofapparatus.

In the construction shown in Figs. 1 to 6 inclusive, 5 represents a worktable such as the table of a planer or milling machine. This table isrigidly secured, as indicated at 6, to the piston rods 1 and 8 ofpistons 9a and 9b working in cylinder I8. The left hand end of cylinderI0 communicates with a port I I which is alternately connected to fluidpressure supply passage I2 and exhaust passage I3 through the agency ofa reversing valve I4. The right hand end of cylinder I0 communicateswith a port I5 which is alternately connected to passages I2 and I3 bythe valve I4. `Passage I2 is connected to a pump or other source ofpressure duid by pipe I6.

Cylinder port is connected, through throttle valve I1 and check valveI9, to valve port 2| leading to reversing valve I4. Cylinder port I5 isconnected, through throttle valve I8 and check valve 20, to valve port22 also leading to reversing valve I4. Check valves I9 and 20 are springloaded to close against the valve seats I9' and 20'. These valves openwhen the flow is from the valve ports 2| and 22 to the cylinder ports IIand I5 respectively, but close when the direction of flow through thecylinder and valve ports is reversed. Throttle valves I1 and I8 arenormally biased to open position by valve springs I1'v and I 8 acting,respectively, against suitable abutments I1a and I8a carried by theouter ends of the valve stems IIb and |8b.r When table 5 approaches theend of its stroke in one direction, an arm 28 acts against the outer endof stem |1b to shift the throttle valve I1 to the right from the lopenposition shown in Figure l. Arm 28 is carried by a pin or shaft 28arotatably mounted in a suitable bracket 29. This pin or shaft 28a isconnected, by arm and vertical link 3|, to one end of a horizontal link32 having its opposite end pivoted to a bracket 33. Link 32 is providedwith a cam lug or projection 34 disposed in the path of an operating camcarried by table 5. When the table 5 approaches the end of its stroke inthe opposite direction the throttle valve I8 is moved inwardly or to theleft by an arm 28b xed to a pin or shaft 28c journalled in bracket 29a.This pin or shaft 28c is connected, by arm 30a and vertical link 3|a, tothe outer end of a horizontal link 32a having its opposite end pivotedto a bracket 33a. Link 32a is provided with a lug 34a disposed in thepath of an operating cam 35a carried by the table.

Reversing valve I4 is slidably mounted in a suitably ported valve liner31 arranged in passage 31a intersecting the main cylinder ports 2| and22; exhaust port I3; and branches |2a and I2b of fluid pressure supplyport I2. The ends of this valve are formed to provide operating pistons38 and 39 working in cylinders 40 and 4I. The body portion of valve I4is provided with annular ports 42, 43, 44 and 45. Port 43 is the portthrough which main cylinder port II is alternately connected to exhaustport I3 or to branch |2a of fluid pressure supply port I2 through valves|1 and I9 and port 2|. The port 44 is the one through which maincylinder port I5 is alternately connected to exhaust port I3 or tobranch I2b of pressure supply port I2 through valves I8 and 20 and port22.

The positioning of reversing valve I4 is controlled by a 'cylindricalpilot valve 41 slidably mounted in pilot valve cylinder 48. Thiscylinder is connected through port 50, valve 5| and port 52 to the uidpressure supply port I2. Valve 5I is normally biased to closed positionby a spring 53 and is automatically opened when uid'pressure in supplyport I2 exceeds a predetermined value. The closing pressure appliedthrough spring 53 is regulated by adjusting screw 54. The ends of pilotvalve cylinder 48 are also connected to the main working cylinder portsII and I5 by suitable pipes 56 and 51. Reversing valve cylinders 40 and4I are also connected to pilot valve cylinder 48 by pipes 59 and 60 andpassages 6I and 62, said passages opening into cylinder 48 at pointsbetween the ends of the cylinder and the central port 50. A port 64,communicating with the extreme left hand end of cylinder 48, isconnected through a valve controlled bypass to a port 65 formed in thecylinder wall below and som-ewhat to the left of the cylinder end ofpassage 6|. Cylinder 48 is also provided with additional ports indicatedat 61 and 68, the former communicating with the extreme right hand endof the cylinder and the latter being located below and slightly to theright of the adjacent end of passage 62. Ports 64 and 55 are connectedtogether by a threeway valve 8U so arranged that when the valve lever isturned to the right as shown, port 64 is blocked and port 65 is openthrough valve 80 to atmosphere. Ports 61 and 68 are similarly connectedby valve 8| except that valve 8|, as shown with the valve lever turnedto the right, affords direct communication between said ports 61 and 68.

In describing the operation it Will be assumed that table 5 and pistons9a and 9b are making a working stroke to the right as indicated by arrow1I. In this case port I of Working-cylinder Il is connected to branchI2a of fluid pressure supply port I2 through annular port 43 ofreversing valve I4 and valves I1 and I9. The remaining working-cylinderport I5 is connected to exhaust passage I3 through annular port 44 ofvalve I4 and valve I8, valve 20 being closed by its spring.

Reversing valve I4 is being held in the position shown in Figure 1partly by pump pressure acting through branch I2b and valve port 45against the annulus X and partly by exhaust pressure acting against theouter face Y of piston 39. In

this connection it will be noted that exhaust pressure in cylinder portI5 is transmitted to the outer end of reversing valve cylinder 4Ithrough pipe 51, valve 8|, port 68, passage 82 and pipe 68. Since valve5I is closed there is no pressure in cylinder 40 of reversing valve I4.Pilot valve 41 is provided with ports 41a and 41b and is held in theposition shown in Fig. 1 by pump pressure admitted to the left hand endof pilot valve cylinder 48 by way of port II, pipe 58 and port 84.

As the table 5 nears the end of its stroke in the direction indicated bythe arrow 1I, cam 35a acting through links 32a, 3Ia and arm 28h servesto partially close throttle valve I8 as shown in Fig. 2. This restrictsthe flow from port I5 to port 22 and causes an immediate rise inpressure in port lI and in the left hand end of cylinder I0 by thepump.v There is a corresponding rise of exhaust pressure in port I5 andthe right hand end of cylinder I0. The increased pressure thusestablished in passage I2 is sufiicient to open valve 5I (Fig. 2) sothat port 58 ls placed in communication with port 52. This permits thepressure in passage I2 to be' transmitted through ports 52, 58, and 41a,passage 6I and pipe 59 to reversing valve cylinder 40 where it actsagainst the outer face Z of piston 38. There is no reversal of valve I4at this time since the pressure acting against the face Z of piston 38is less than the sum of the opposing pressures acting against annulus Xand face Y of piston 39, due to the rise in exhaust pressure in port I5,pipe 51, valve BI, ports 68, 41h and 62 and pipe 60.

As piston 9b reaches the end of its stroke (Fig. 3) and is held againstfurther movement by engagement of table 5 with the right hand table stop5a, the pressure in port I5 and reversing valve cylinder 4I drops to thepoint where the pump pressure acting against the face Z of piston 38overcomes the pump pressure acting on annulus X and becomes effective toshift valve I4 to the right as indicated in Fig. 3. In `this connectionit will be noted that the pressure receiving area Z is larger than thearea X. It may be noted here that when piston 9a reaches the positionshown in Fig. 3 valve I8 is fully closed so that port I5 is isolatedfrom port 22.

When valve I4 reaches to the extreme right hand position shown in Fig. 4pressure fluid is supplied tothe right hand end of cylinder I8 throughports I2, 44, 22, I5, and valve 28 and is exhausted from the left handendof said cylinder through ports II, 2|, 43 and I3 and valve I1. As cam35a moves away from link 32a on the return stroke of piston 9 cushioningvalve I8 resumes its open position as shown in Fig. 4.

During the aforesaid reversal of valve I4 valve 5I closes and the righthand end of pilot valve cylinder 48 is connected to port I2 through port61, pipe 51 and ports I5, 22 and 44. The left hand end of pilot cylinder48 is simultaneously connected to exhaust port I3 through port 64, pipe56, port II, valve I1, and ports 2| and 43. Pump pressure is thusestablished in the right hand end of cylinder 48 and acts to shift valve41 to the left. (Fig. 4.) This disrupts the communication previouslyestablished between pilot valve cylinder ports 58 and 6I through pistonport 41a and places port 50 in communication with port 62 through pistonport 41h as shown more particularlyin Fig..4.

`As` pistons 9a and 9b near the end of their `return stroke cam 35engages lug 34 and operates link 32 to shift cushioning valve I'I to theright, thus throttling the exhaust through port Il. The resulting risein pump pressure in port I2 opens valve 5| so that port 50 is connectedto port I2 through port 52. Since pilot valve 41 is now in the positionshown in Fig. 4', port 50 is also connected to port 62 through pistonport 41h so that pump pressure is established in cylinder 4I and actsagainst the face Y of piston 39 to shift reversing valve I4 to the left.Since valve cuts off port 84 and exhausts ports B5 and 6I through port41a there is no exhaust pressure acting against piston 38 in oppositionto the pump pressure acting against piston 39. Consequently, valve I4will reverse as soon as the pump pressure in port I2 is increased by theexhaust throttling action of valve I1.

From the foregoing it will be seen that table 5 operates againstmechanical stop 5a at the end of the working stroke and against ahydraulic cushion at the end of the return stroke. On the Working strokethe pressure conditions necessary for operating the reversing valve areestablished partly by the increased pump pressure due to choking of theexhaust near the end of the working stroke and partly by the drop inexhaust pressure which occurs in part of the system as the piston ishalted by the stop 5a. This arrangement enables the reversal of table 5at the end of the working stroke to be predetermined within very nelimits. On the return stroke the reversal is timed solely bythethrottling action of valve I1 which, in addition to providing ahydraulic cushion against which the table 5 operates, also causes therise in pump pressure which acts against piston 39 to reverse valve I4.This method of effecting reversal of the table at the end of the returnstroke is satisfactory where it is not necessary for the table to workto a ne clearance at both ends of its travel. It will be understood,however, that the return stroke of table 5 may be adjusted, withinlimits, by changing the position of the cam 35.

If it is desired to have table 5 operate against a mechanical stop ateach end of its travel this may be accomplished by providing the lefthand table stop 5b and reversing the position of valve 80 to provide acommunicating passage between ports 64 and 65, valve 8l being left inthe position shown in the drawings. In this case throttling of port IIby valve I'I does not result in immediate reversal of valve I4 from theposition shown in Fig. 4. On the` contrary, exhaust pressure transmittedto the face Z of piston 38, through pipe 56, valve 80, ports 41a and 6Iand pipe 59 serves, in conjunction with the pump pressure acting againstannulus X' (Fig. 4) to hold valve I4 against reversal until table 5encounters stop 5b. When this occurs the resulting drop in exhaustpressure acting against face Z permits the pump pressure acting againstface Y of piston 39 to overcome the pump pressure acting against annulusX' and thus effect reversal of valve I4. i

If it is desired to provide for instant reversal of the table at bothends of travel without the use of the mechanical stops 5a and 5b thismay be accomplished by leaving valve 80 in the position shown in Fig. land reversing valve 8| to a position blocking port 61 and venting port88 to atmosphere. This prevents exhaust pressure being established ineither of the cylinders 40 and 4I. Thus any degree of accuracy in eitherdirection may be had at the will of the operator.

Fig. 7 shows a modification in which provision is made for operating twotool slides alternately. In this case cylinder ports II and I5 are-through ports I2, I| and I5.

respectively connected to the outer ends of cylinders 14 and 15. Thesecylinders contain the working pistons 16 and 11 to which the tool slides18 and 1 9 are rigidly fastened as indicated at 80. The ports II 4and-I5 are alternately placed in communication with pressure supply passageI2 and exhaust passage I3 through the agency of the main reversing valveI4 and pilot valve 48. In this instance the cushioning valve I1 isomitted from passage II.

The pistons 16 and 11 are operated on their inward or working strokes byhigh pressure uid pumped to the outer end of cylinders 14 and 15 Ontheir return stroke the pistons are operated by a relatively low,constant, push-back pressure obtained from a separate source such as anair loaded accumulator connected to the inner ends of cylinders 14 and15. In Fig. '7 pipe 82 represents a push back pressure supply leadingfrom the accumulator 82a. This pipe is provided with branches 83 and 84communicating with pressure chambers 85 and 86 formed in the cylinderheads 14a and 15a of cylinders 14 and 15. Chamber 85 is in constantcommunication with cylinder 14 through the port 81 and bore 88 of ahollow stop pin 89. This pin is slidably mounted in cylinder head 14a.so that its inner end projects into the inner end of cylinder 14.Chamber 85 and cylinder 14 are also connected by a bypass 90 providedwith a check valve 9|.

Chamber 86 is in constant communication with cylinder I5 through theport 93 and bore 94 of a hollow stop pin 95 slidably mounted in cylinderhead 15a so that its inner end extends into said cylinder. Chamber 86and cylinder 15 are also connected by a bypass 96 provided with a checkvalve 91.

The outer ends of pins 89 and 95 serve as piston stops which t into thepiston recesses 16a and 11a as the pistons 15 and 16 complete theirworking strokes, the length of which may be accurately predetermined bylengthwise adjustment of the pins 89 and 95 with reference to cylinders14 and 15. In the present instance each stop pin is adjusted by means ofan adjusting screw in threaded engagement with the wall of the pin bore,said screw being keyed to a worm wheel |02 which is held againstlongitudinal movement in a gear casing |03 and is operated by a suitableworm |04. The outer ends of pins 89 and 95 are also provided withlateral slots 89a and 95a which serve to maintain restrictedcommunication between the bores of the pins and the inner ends ofcylinders 14 and 15 when the pistons 16 and 11 are at the ends of theirworking strokes. These slots are tapered so that they decrease in widthtoward the inner ends of the pins.

The pilot valve cylinder ports 66 and 68 are respectively connected tothe inner ends of cylinders 14 and 15 by pipes |04 and |05. Theremaining pilot valve cylinder ports are connected in the same way asdescribed in connection with Fig. 1, with the exception that ports 64and 69 are both plugged as indicated at |08'.

In Fig. 7, piston 11 is shown at the end of its working stroke, theouter end of cylinder 15 being .connected to the iluid pressure supplypassage I2 through cylinder port I5 and reversing valve port 44. As thepiston is stopped by pin 95 the pump pressure in passage I2 rises andopens valve I so that reversing valve cylinder 4I is placed incommunication with port I2 through ports 52, 50, 41b and 62 and pipe 60.Pump pressure is thus established in cylinder 4| and acts against theface Y of reversing valve piston 89.

Valve I4 does not reverse at this time because the pressure in cylinder4| ls insufilcient to overcome the corresponding increase ot theopposing push back pressure which is-transmitted from the push backannulus |08 of cylinder 15 to reversing valve cylinder 40 through pipe|05, pilot valve ports 41a and 8| and pipe 59. In this connection it maybe explained that the escape of push back pressure from annulus |08 isthrough the bore of pin 85 and is choked or throttled as the inner endof this pin enters the piston recess 11a. When piston 95 comes to restthe extreme inner end of the pin port v95a is still uncovered by thepiston and provides restricted communication between annulus |05 and thebore oi pin 85. By virtue of this communication, the push back pressurein annulus |08 drops to normal as soon as the piston is halted by pin 95and this drop is sulcient to permit reversal of valve I4 by the pumppressure acting against face Y of reversing valve piston 39. When valveI4 is reversed iiuid pressure is exhausted from the outer end ofcylinder 15 through cylinder port I5, reversing valve port 44 andexhaust passage I3. This permits the piston 11 to be operated on itsreturn stroke by push back pressure supplied to the inner end ofcylinder 15 through pin 95 and bypass 91. The purpose of the bypass 91is to speed up the return stroke of the piston by permitting a morerapid flow of the push back pressure into the cylinder 15 than would bepossible if all the push back pressure had to enter the cylinder throughpin 95. I'he bypass 91 is not essential and may be `omitted wherespeeding up of the return stroke is unimportant.

When valve I4 is reversed to connect cylinder port I5 to exhaust passageI3, the cylinder port II is connected to receive pressure fluid fromport I2 through reversing valve port 43. At the same time theconnections at the reversing valve ends of pilot valve passages 56 and51 are reversed so that passage 56 is now connected to fluid pressuresupply port I2 through cylinder port II and reversing valve port 43while passage 51 is connected to exhaust passage I3 through cylinderport I5 and reversing valve port 44. Pump pressure is thus establishedin the left hand end of pilot valve cylinder 41 to shift pilot valve 48to the right. This shifting of valve 48 disrupts communication betweenpipe |05 and pilot Valve port 6I and establishes communication betweenpilot valve port 62 and the pipe |04 which is connected to the inner endof cylinder 14. The reversal of valve 48 also disrupts the communicationpreviously established between pilot valve ports 50 and 62 and placesport 50 in communication with pilot valve port 6| which is connected toreversing valve cylinder 40 as previously described.

With cylinder port I5 connected to exhaust port I3 and cylinder port IIconnected to pressure fluid supply port I2 by the described reversal ofvalve I4 the piston 16 will make a working stroke under pump pressuresupplied through passage II as the piston 11 makes its return strokeunder push-back pressure supplied from accumulator 82a through pipes 82and 84, chamber 86, pin 95 and valve 91, such push-back pressure actingagainst piston 11 being increased to some extent by the discharge fromcylinder 14 into the push-back pressure system. The return speed ofpiston 11 depends on the resistance offered by the work to the toolcarried by toolslide 19. When piston 16 nears the end of its workingstroke the escape of the push back pressure` through pin 89 is choked asthe inner end of the pin enters the piston recess 16a. The workingstroke of piston 16 is thus cushioned and slowed/ down so that there isan immediate rise in both the pump pressure and the push back pressurein cylinder 14. The rise of pump pressure in port I2 issufficient toopen valve 5| so that port is placed in communication with reversingvalve cylinder 40 through ports 52, 50, 41a, 6| and pipe 59, it beingremembered that pilot valve 48 is now in the opposite position to thatshown in Fig. 7. The pump pressure thus established in reversing valvecylinder 40 becomes effective to shift valve |4 to the right when theopposing push back pressure in reversing valve cylinder 4| drops tonormal as occurs when piston 16 is halted by pin 89. In this connectionit will be noted that When pilot valve 48 is in the opposite position tothat shown in Fig. '1 the push back pressure in annulus of cylinder 16is transmitted to reversing valve cylinder 4| through pipe |04, pilotvalve ports 66, 41h and 62 and pipe 60. When valve |4 is reversed toresume the position shown in Fig. 7 the pilot valve 48 is also returnedto the position shown in this ligure by pump pressure acting throughpassage 51.

Having thus described my invention, what I claim is:

1. Apparatus for operating a machine tool or other translatable elementby fluid pressure comprising means for applying working fluid pressureto move said element in a given direction against an opposing fluidpressure, means for increasing the opposing pressure to effect acorresponding increase of the working pressure when the element hastravelled a predetermined distance, and means for reversing thedirection of travel of the element in response to the increase of theworking pressure.

2. Apparatus for operating a machine tool or other translatable elementby fluid pressure comprising a mechanical stop, means for applying fluidworking pressure to move said element toward said stop against theresistance of an opposing fluid pressure, means for automaticallyincreasing said opposing pressure to effect a corresponding increase ofthe working pressure when the element has travelled a predetermineddistance toward said stop, means for reversing the direction of travelof the element in response to said increase of working pressure, andmeans for preventing operation of said last mentioned means until theelement is halted by said stop.

3. Apparatus for operating a machine tool or other element by fluidpressure comprising means for applying working pressure to move saidelement in a given direction against an opposing pressure, means forincreasing the opposing pressure to cause a corresponding increase oftheworking pressure when the element has travelled a predetermineddistance, means for reversing the direction of travel of the element inresponse to the increase of working pressure and means for utilizingsaid opposing pressure to prevent operation of the reversing means untilthe element has travelled to a predetermined point beyond the point atwhich the pressure increase occurs.

4. Apparatus for operating a machine tool or other translatable elementby fluid pressure comprising a mechanical stop, means for applying fluidpressure to move said element into engagement with said stop against theresistance of an opposing iluid pressure, means for increasing theopposing pressure to cause a corresponding increase of the workingpressure when the element has travelled a predetermined distance towardsaid stop, means for reversing the direction of.

travel of the element in response to the said increase of workingpressure and means for utilizing said opposing pressure to preventoperation of the reversing means until the element is halted byengagement with said stop.

5. Apparatus for operating a machine tool or other element by iluidpressure comprising a mechanical stop. means for applying workingpressure to move said element into engagement with said stop against theresistance of an opposing fluid pressure, means for increasing theopposing pressure to cause a corresponding increase of the workingpressure when the element has travelled a predetermined distance towardsaid stop, a reversing valve arranged to operate in response to theincrease of working pressure to establish connections resulting inreversal `oi! the direction of travel of said element and means forutilizing said opposing pressure to prevent the aforesaid operation ofthe reversing valve until the element is halted by engagement with saidstop.

6. Apparatus for operating a machine tool or other element by lluidpressure comprising means for applying working fluid pressure to movesaid element in a given direction against an opposing uid pressure,means for increasing the opposing pressure to cause a correspondingincrease of the working pressure when the element has travelled apredetermined distance and a reversing valve arranged to operate inresponse to the said increase of working pressure to establishconnections resulting in reversal of the direction of travel of thetool.

7. Apparatus for operating a machine tool or other element by fluidpressure comprising means for applying working fluid pressure to movesaid element in a given direction, means for increasing said pressurewhen the element has travelledv a predetermined distance, a reversingvalve, means functioning in response to the said increase of workingpressure for opening a normally closed passage through which saidpressure is applied directly to the reversing valve to operate thelatter to a position establishing connections resulting in reversal ofthe direction of travel of said element and means for preventing theaforesaid operation of the reversing valve in response to the opening ofsaid passage until said element has travelled a predetermined distancebeyond the point at which the pressure increase occurs.

8. Apparatus for operating a machine tool or other element by fluidpressure comprising a cylinder, a piston working in the cylinder andconnected to said tool or other element, a reversing valve through whichfluid working pressure is applied to one side of the piston to move thetool or other element on a working stroke against an opposing fluidpressure acting against the opposite side of the piston, a valve throughwhich said opposing fluid pressure is discharged from the cylinderduring the aforesaid movement oi' the piston, means for operating saidvalve to throttle the discharge of said opposing pressure from saidcylinder when the tool has been moved a predetermined distance on itsworking stroke, said operation of the valve serving to increase effect areturn movement of the tool at the endof the working stroke and a valvenormally closing said passage and arranged to be opened automatically bythe working pressure when the latter is increased to a predeterminedvalue by the aforesaid increase of the opposing fluid pressure.

WILLIAM P. MUIR.

